This invention aids the characterization of microwave devices and circuits and more particularly relates to a digitally controlled microwave impedance network for producing a plurality of complex impedances.
The characterization of microwave devices and circuits is often accomplished by terminating the device in a network consisting of a combination of existing components such as variable tuners, attenuators and phase shifters which must be calibrated together and provided with some means of resetting their adjustments to the previously calibrated position; such adjustments are usually continuous. For high power applications, some of the readily available components are unsuitable because of their power sensitivity or limitations. The characterization of non-linear power transistors and low noise linear transistors both require measurements to be made under various loading conditions. Computer control of these measurements is attractive not only from the point of view of data collection and manipulation, but also in the equipment control that it provides.
There are two essentially different approaches to the characterization of load dependent devices. One is to adjust the load until some performance criteria are met; the other is to measure the performance for various known loading conditions and then establish their relationships. This second method is better suited to digital control because it requires a finite number of discrete states of loads (which can be calibrated) rather than continuous variability.